How to tell bad alternator or bad battery problem?

Telling a bad alternator vs bad battery will be the main option if you have a charging problem with your car. This problem is started when your car wont start clicking noise, the dashboard lights are dim, and the engine wont runs as usual. Yes, the alternator and battery are the main components for the charging system, but it's related to the starting system.

There are three simple steps for the charging system to work:

The battery sends a jolt of electricity to the starter motor.
The starter motor runs the engine, which puts the alternator into action.
The alternator charges the battery to keep a jolt of electricity to start the starter motor.

With these cycles, the availability of electric current inside the battery can be fulfilled to start the starter motor. If the battery makes the car won't start the engine, which one is to choose, a bad alternator or bad battery?

This article will give you information on how to tell a bad alternator vs bad battery when the problem occurs. See the way below.

I. Start and run your car engine first

Before deciding between a bad alternator vs bad battery, we have to start and run your car engine first. Since the alternator and the battery are working together inside the charging system, they actually work alternately.

The battery is mostly used when the engine is off, while the alternator is used when the engine run. So, to know which is in bad condition, we need to start and run your car engine first.

Do a jump-start car battery (you can read it on how to jump-start a car). It is better than we buy a car battery or alternator before we know which one is bad.

Note:

When your car engine is already running, pay attention when you remove the jumper cables out from your car battery and see the signs that come out from your car below.

II. See the signs that come out from your car

Several signs commonly appear to tell if it's a bad alternator vs bad battery after you jump start a car battery. See the common symptoms of each component below :

1. Common signs of a bad alternator

Your car engine stops immediately after removing the jumper cables from your car battery.
The battery warning lamp at your dashboard panel is turned on.
While the engine runs, turn on the headlamps and see the lights—bad alternator resulting dim light in idling engine rpm and get brighter when we raise the engine rpm.
Weird smells come out from the alternator.
Strange sounds were heard from the alternator, such as growling or grinding noises.

For more detailed information, please read #5 Signs of car alternator problem that I've written before.

2. Common signs of a bad battery

It's impossible to start over your engine after you shut off the engine. A bad battery can't use to crank the engine.
You can see the dashboard lights are dim when you turn the ignition key to the ON position.
The physical condition of the battery looks bad such as bloated, leakage, or corroded terminal battery.

For more detailed information, read the #5 Signs your car battery is dead to ensure the car battery is bad.

III. Test each component with proper tester tools.

Even the signs are commonly used to make a decision for bad alternator vs bad battery and which is the bad component. You must do proper measurement for those components with a proper tester tool. Mostly, we can measure a bad alternator or a bad battery with a digital multimeter. Still, it would be best if you had several measurement tools for better results.

1. Checking the alternator

There are two ways on how to check the alternator. First, you can check the alternator without a multimeter (not recommended). Second, test the alternator with a digital multimeter and ampere meter (highly recommended). Both ways can be used o check the alternator. The risk is at yours.

Here are some recap for testing an alternator with a tester tool

The alternator is going bad if the output voltage is less than 13.50 Volt (Undercharge) or more than 14.70 Volt (Overcharge).
The alternator is going bad if the output amperage is less than 50% from the max output voltage of the alternator specification.

2. Checking the battery

The simplest way to check the battery is with a digital battery tester. Still, you also can use the digital multimeter either. Read #2 ways on how to check a car battery.

Here is a recap for checking the battery voltage with a multimeter.

The battery is going bad if the voltage measured is less than 11 volt. It means that the battery is in a discharged state.

Testing each component (battery and alternator) with a proper tester tool is the best way to tell which is bad, alternator or battery.